Lasers are used on a large scale for material processing, for example for welding and cutting. For this purpose, the laser beam has to be passed over the workpiece. This may occur by moving a processing head relative to the workpiece. In this respect, the movement speed and hence also the processing speed are limited by the mass of the processing head or the mass of the workpiece. A higher processing speed may be achieved using processing heads having movable optical deflection units, for example rotatable mirrors, by means of which the laser beam is passed over the workpiece. Systems of this type are referred to as scanning systems.
A scanning system of this type may also be guided by a robot which then carries out a rough positioning. The scanning system which is clearly more dynamic than the robot carries out the fast and precise fine positioning of the focus.
Scanning systems of this type require that the position and the size of the focus should be completely under control during the processing. In this respect, it may, for example, be desirable to have a constant size of the focus, for example provided by its diameter, over the entire working area of the scanning system, independent of the driven focus position. Moreover, it may, for example, be desirable to be able to change the focus size specifically, depending on the processing requirements.
In addition, there is a requirement in scanning systems of this type to have outer dimensions which are as compact as possible. For example, it may be desirable to immerse in a workpiece with a complex shape using the robot-controlled scanning system, in order to carry out a laser processing therein in an inaccessible place. This is much easier the more compact the structure of the scanning system is.